MATERIALS & PROPERTIES ·
A4-70 vs A4-80 Bolts: differences, mechanical properties and applications
The main difference between A4-70 and A4-80 stainless steel bolts concerns their mechanical properties, not the stainless steel family.
Both belong to the A4 austenitic stainless steel family, but according to ISO 3506-1, A4-70 has a minimum tensile strength of 700 MPa, while A4-80 reaches 800 MPa.
This distinction is important when selecting screws, bolts and studs for industrial applications.
What does A4-70 mean?
The A4-70 designation identifies two characteristics:
- A4: the family of molybdenum-containing austenitic stainless steels, commonly associated with 316-type stainless steels.
- 70: the mechanical property class, corresponding to a minimum tensile strength of 700 MPa.
A4-70 fasteners combine the corrosion-resistance characteristics of A4 stainless steels with the mechanical requirements specified for property class 70.
What does A4-80 mean?
A4-80 also belongs to the A4 family of austenitic stainless steels, but it must meet higher mechanical strength requirements.
The designation identifies:
- A4: the stainless steel family.
- 80: the mechanical property class, corresponding to a minimum tensile strength of 800 MPa.
In austenitic stainless steels, the increase in strength is normally achieved through a higher degree of cold working.
A4-80 therefore represents a higher mechanical property class within the same stainless steel family.
Mechanical differences between A4-70 and A4-80
| Property | A4-70 | A4-80 |
|---|---|---|
| Minimum tensile strength | 700 MPa | 800 MPa |
| Minimum stress at 0.2% non-proportional elongation | 450 MPa | 600 MPa |
| Minimum elongation after fracture | 0.4 × d | 0.3 × d |
| Stainless steel family | A4 | A4 |
Note: elongation after fracture is expressed in millimetres as a function of the nominal diameter d; it is not a percentage.
The values must be interpreted according to the scope and requirements of the standard.
The higher strength of A4-80 does not automatically mean that it can replace A4-70 in every bolted connection.
Is A4-80 more corrosion resistant?
Not necessarily.
Both property classes belong to the A4 family. The main distinction concerns their mechanical properties.
Actual corrosion resistance also depends on chemical composition, surface condition, manufacturing processes and the service environment.
When selecting fasteners, mechanical requirements and corrosion-resistance requirements should therefore be evaluated separately.
When should A4-70 or A4-80 be selected?
A4-70 can be used when its mechanical characteristics satisfy the requirements of the design.
A4-80 can be considered when higher minimum tensile strength and 0.2% proof stress values are required.
The selection must also consider dimensions, geometry, loads, installation conditions and applicable standards.
The mechanical property class alone does not define tightening torque, fatigue resistance or the suitability of the complete bolted connection.
Is A4-80 available in every diameter?
ISO 3506-1:2020 covers, within its scope, screws, bolts and studs with metric thread up to M39.
For larger dimensions, the grade and property class designations specified by the standard may be used provided that all applicable chemical, mechanical and physical requirements are satisfied and verified.
For special fasteners and large diameters, it is therefore important to confirm the achievable characteristics in advance.
What information is needed to request a quotation?
A quotation request for A4-70 or A4-80 fasteners should specify:
- Product type and DIN/ISO standard or technical drawing
- Diameter, pitch and length
- Required material and mechanical property class
- Quantity
- Any required certificates and documentation
- Any additional dimensional, application or surface requirements
A complete specification makes it possible to identify the requested product correctly.
Mechanical testing and quality verification at Anchor Pro
At Anchor Pro, we perform tensile tests to fracture internally on fastener samples to verify their mechanical performance, while information concerning the chemical composition of the materials comes from the documentation supplied by our raw-material suppliers.
This approach combines direct mechanical testing with documentation supporting material traceability.
A4-70 and A4-80 fasteners from Anchor Pro
Anchor Pro operates in the industrial fastener sector, including the supply of stainless steel components manufactured according to DIN/ISO standards and customer technical drawings.
To request a quotation, dimensions, material, mechanical property class, quantity and any documentation requirements can be provided.
Contact Anchor Pro to submit your technical specifications and request a quotation.
Need A4-70 or A4-80 fasteners for your application?
Send your dimensions, material, mechanical property class, quantity and documentation requirements to Anchor Pro.